Mercury-free sensor rapidly detects heavy metals in humans

University of Cincinnati's new manganese detector is designed to deliver results in about 10 minutes. Photo: Dottie Stover

Work
by University of Cincinnati researchers to create a sensor that
provides fast feedback related to the presence and levels of heavy
metals?specifically manganese?in humans is published in the August issue
of the journal Biomedical Microdevices.

Described
in the article is the development of a low-cost, disposable
lab-on-a-chip sensor that detects highly electronegative heavy metals
more quickly than current technology generally available in health-care
settings. It’s envisioned that the new UC sensor technology will be used
in point-of-care devices that provide needed feedback on heavy-metal
levels within about ten minutes.

It’s
expected that the sensor will have potential for large-scale use in
clinical, occupational and research settings, e.g., for nutrition
testing in children.

The
new sensor is environmentally friendly in that its working electrode is
made of bismuth vs. the more typical mercury, and it’s child friendly
in that it requires only a droplet or two of blood for testing vs. the
typical five-milliliter sample now required.

Explained
one of the researchers, UC’s Ian Papautsky, “The conventional methods
for measuring manganese levels in blood currently requires about five
milliliters of whole blood sent to a lab, with results back in 48 hours.
For a clinician monitoring health effects by measuring these levels in a
patient’s blood – where a small level of manganese is normal and
necessary for metabolic functions – you want an answer much more quickly
about exposure levels, especially in a rural, high-risk area where
access to a certified metals lab is limited. Our sensor will only
require about two droplets of blood serum and will provide results in
about ten minutes. It’s portable and usable anywhere.”

One
specific motivation for developing the sensor was an ongoing project by
UC’s Erin Haynes, who is studying air pollution and the health effects
of manganese and lead in Marietta, Ohio. Manganese is emitted in that
area because it is home to the only manganese refinery in the United
States and Canada. Preliminary results from UC’s Mid-Ohio Valley Air
Pollution Study (M.A.P.S.) found elevated levels of manganese in
Marietta residents when compared to those who live in other cities.

How the UC sensor works

The disposable heavy metal sensor is of a small size. Photo: Dottie Stover

The
new UC sensor uses a technology called anodic stripping voltammetry
that incorporates three electrodes: a working electrode, a reference
electrode and an auxiliary electrode.

A
critical challenge for such sensors is the detection of electronegative
metals like manganese. Detection is difficult because hydrolysis, the
splitting of a molecule into two parts by the addition of a water
molecule, at the auxiliary electrode severely limits a sensor’s ability
to detect an electronegative metal.

To
resolve this challenge, the UC team developed a thin-film bismuth
working electrode vs. the conventional mercury or carbon electrode. The
favorable performance of the bismuth working electrode combined with its
environmentally friendly nature means the new sensor will be especially
attractive in settings where a disposable lab-on-a-chip is wanted.

In
addition, the UC team also optimized the sensor layout and
working-electrode surface to further reduce the effects of hydrolysis
and to boost the reliability and sensitivity in detecting heavy metals.
The new sensor layout better allowed for its functioning, which consists
of taking of a blood serum sample, stripping out the heavy metal and
then measuring that heavy metal.

The
end result is the first lab-on-a-chip able to consistently pinpoint
levels of highly electronegative manganese in humans. The new sensor
also exhibits high reliability over multiple days of use, with hours of
continuous operation. With further developments, the chip may even be
converted into a self-check mechanism, such as with glucose screening
for diabetics.

Funding
for this research has been provided by the National Institute of
Environmental Health Sciences, the National Institute of Occupational
Safety and Health Pilot Research Project Training Program and the
University of Cincinnati.